1. Field of the Invention
The invention relates to an image forming apparatus using an electrophotographic process such as, for example, a printer or a copying machine.
2. Description of the Related Art
Generally in an image forming apparatus utilizing an electrophotographic printing method, a photoconductive drum and a cleaner and a developing unit around the drum are made into a unit, which in turn is constructed so as to be interchangeable with respect to a printer main body, i.e., an image forming apparatus main body. This unit is expendables and need be interchanged when its life expires. In order to inform a user that the interchange of the unit is necessary, the printer has a rotary part, e.g. a counter for counting the cumulative number of revolutions of the photoconductive drum. When the count value of the counter reaches a predetermined value, the printer displays a life alarm indicating that the interchange of a corresponding unit is necessary. By this alarm, the user can interchange the unit at an appropriate time.
When an old unit is interchanged with a new unit, it is necessary to reset a counter for measuring the life of the photoconductive drum, and change charging potential to be applied in accordance with a new drum, and a table for converting image data into density information.
In a conventional image forming apparatus, there has been proposed a method of disposing a non-volatile memory in a unit, and causing the memory to store a history of use therein, thereby detecting whether the unit is new or old (Japanese Patent Application Laid-open No. H09-185236). In a color image forming apparatus having a plurality of such units (drum units), however, it is necessary to dispose a memory in each unit and at the same time, it is necessary to dispose a communicating portion with the memory at a location whereat each unit and an image forming apparatus main body are in contact with each other. Therefore, the costs of the apparatus and the unit have become high, and there has also been a problem in respect of the apparatus size and unit disposition.
In contrast, there has been proposed a method of judging by a fuse provided on a unit (drum unit) whether the unit is new or old (Japanese Patent Application Laid-open No. H05-61393 and Japanese Patent Application Laid-open No. H06-118736). This method is to detect the conducting state of the fuse of the unit mounted on an apparatus main body to thereby judge whether the unit is new or old, and when it judges the unit to be new, carry out a predetermined initializing process and cut the fuse. That is, an inexpensive fuse instead of a memory can be provided on the drum unit, and a unit new/old discriminating portion for detecting whether an electric current passes through the fuse, and a fuse fusing portion for supplying an overcurrent to the fuse can be provided in the apparatus main body. The unit new/old discriminating portion and the fuse fusing portion are both constituted by a relatively simple circuit and can therefore discriminate between the newness and oldness of the unit (drum unit) by inexpensive and simple structure.
However, the following problem arises when design is made such that as described above, the conducting state of the fuse provided on the unit is detected to thereby judge whether the unit is new or old, and when the unit is judged to be new, a predetermined initializing process is carried out and the fuse is cut.
For example, when a problem has arisen in an image formed by the image forming apparatus, it is necessary to discriminate whether the cause of the problem resides in the image forming apparatus main body or in the drum unit. Therefore, a serviceman or the user himself sometimes tries to mount a new drum unit on trial on an image forming apparatus main body in which a problem has arisen and check up the operation thereof. In this case, when the new drum unit is put into the apparatus, the image forming apparatus detects the newness of the drum and automatically performs the operation of initializing the drum, and adjusts a parameter in the interior of the machine to a state optimum for the new drum unit and also burns out the fuse of the drum unit. Thereafter, it outputs an image and checks up the operation, and if as the result, it is discriminated that the cause resides in the drum unit so far mounted, the new drum unit can be intactly used.
However, if conversely, it has been found that the cause resides in the image forming apparatus main body, a normal drum unit originally mounted on the apparatus becomes useless. That is, even if an attempt is made to return the normal drum unit originally mounted on the apparatus into the apparatus and use it, the control parameter has already been initialized so as to be optimum for the new drum unit at a point of time whereat the new drum unit has been mounted as a test. Therefore, the image forming apparatus cannot be used in a state optimum for the normal drum unit originally mounted on the apparatus. Also, the new drum unit used on trial has had its fuse cut and therefore, is not recognized as a new one even if it is newly mounted on other apparatus. Therefore, the initializing operation is not performed and the apparatus cannot be used in an optimum state.